Sleep apnea occurs when a subject periodically stops breathing or has diminished breathing during sleep. Oral appliances may be used in the treatment of sleep apnea. Oral appliances may have a mandibular portion that contacts one or more mandibular teeth of a subject in an as-used position inserted into the mouth of the subject and a maxillary portion that contacts one or more maxillary teeth of the user when in the as-used position. Oral appliances for treatment of sleep apnea may be configured to provide mandibular advancement of the subject for opening obstructions of the subject's upper airway.